CAPE CANAVERAL — Threatened with cancellation four years ago, NASA's Orion capsule survived the political heat.

This week, NASA will see if the spacecraft it is designing to one day fly astronauts to Mars can handle a searing, 20,000-mph re-entry through Earth's atmosphere during its first test flight.

At 7:05 a.m. ET Thursday, an unmanned test capsule is scheduled to blast off from Cape Canaveral Air Force Station atop a Delta IV Heavy rocket to begin a two-orbit, four-and-a-half hour mission called Exploration Flight Test-1.

"EFT-1 is absolutely the biggest thing that this agency is going to do this year," said Bill Hill, NASA's deputy associate administrator for Exploration Systems Development. "This is really our first step on our journey to Mars."

That is the hope for the spacecraft NASA has already spent eight years and more than $9 billion developing, with at least seven more years to go before astronauts climb on board.

A successful test flight will boost the agency's morale three years after the last shuttle launch, and show progress that could help solidify Orion's long-term future.

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The Orion capsule is moved from the high bay in the Neil Armstrong Operations and Checkout Building to the Payload Hazardous Servicing Facility, where it will be fueled for its December flight. Craig Bailey/FLORIDA TODAY

KSC Director Robert Cabana and Orion Program Manager W. Michael Hawes watch as the Orion capsule is moved from the high bay in the Neil Armstrong Operations and Checkout Building to the Payload Hazardous Servicing Facility. Craig Bailey/FLORIDA TODAY

KSC Director Robert Cabana and Orion Program Manager W. Michael Hawes watch as the Orion capsule is moved from the high bay in the Neil Armstrong Operations and Checkout Building to the Payload Hazardous Servicing Facility. Craig Bailey/FLORIDA TODAY

Scott Wilson, Orion Production Operations Manager speaks as the Orion capsule is moved from the high bay in the Neil Armstrong Operations and Checkout Building to the Payload Hazardous Servicing Facility. Once there, it will be fueled for its December flight. Craig Bailey/FLORIDA TODAY

The Orion capsule is moved from the high bay in the Neil Armstrong Operations and Checkout Building to the Payload Hazardous Servicing Facility, where it will be fueled for its December flight. Craig Bailey/FLORIDA TODAY

The Orion capsule is moved from the high bay in the Neil Armstrong Operations and Checkout Building to the Payload Hazardous Servicing Facility, where it will be fueled for its December flight. Craig Bailey/FLORIDA TODAY

The Orion capsule is moved from the high bay in the Neil Armstrong Operations and Checkout Building to the Payload Hazardous Servicing Facility, where it will be fueled for its December flight. Craig Bailey/FLORIDA TODAY

The Orion capsule is moved from the high bay in the Neil Armstrong Operations and Checkout Building to the Payload Hazardous Servicing Facility, where it will be fueled for its December flight. Craig Bailey/FLORIDA TODAY

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But even if it successfully soars 3,600 miles up — higher than any craft intended to carry humans in more than 40 years — and splashes down in the Pacific Ocean, Orion will continue to grapple with tight funding, technical challenges, bureaucracy and political uncertainty that have slowed its progress so far.

Orion today is overweight and still searching for missions. There is no funding yet for a habitat module that could extend its missions beyond a few weeks, or for a lander to place astronauts on another surface.

After this flight, Orion will depend for rides on the huge Space Launch System rocket NASA is developing. Its first test launch from Kennedy Space Center has been delayed a year, to 2018, with a first manned flight possible by 2021 and no confirmed flights after that.

The head of NASA's Orion spacecraft project says they've always known the risks associated with space travel. The recent explosion of Orbital Sciences' Antares rocket hasn't changed plans for Orion's December launch.

Without increases to the flat budgets anticipated in the coming years, an independent review this year concluded there's no chance astronauts in Orion will reach Mars by the 2030s.

"Obviously this launch is a stepping stone forward to whatever might happen beyond low Earth orbit," said Jonathan Lunine, a Cornell University professor who co-chaired the National Research Council's "Pathways to Exploration" study.

However, he added, the study concluded that "the current program as it's constituted will, if nothing changes, reach a dead end."

Here's an overview of Orion's journey so far, and where it might be going.

Q. What is Orion?

After 30 years circling in low Earth orbit with the space shuttle, Orion represents NASA's attempt to return astronauts to deep space, with the moon, an asteroid and eventually Mars as potential destinations.

After the Columbia shuttle disaster in 2003, President George W. Bush unveiled a new strategy to retire the shuttle and return astronauts to the moon. The Apollo-like Orion capsule and two Ares rockets emerged as the centerpieces of NASA's Constellation program.

By 2009, a White House panel found that Orion's Ares I rocket was years behind schedule, as was any moon mission. It said NASA needed billions more annually to sustain a viable human exploration program.

The Obama administration called for a reboot, canceling Constellation. NASA would focus on developing low-cost private spacecraft to taxi astronauts to the International Space Station, and on technologies that could make deep space missions safer and more affordable.

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The head of NASA's Orion spacecraft project says they've always known the risks associated with space travel. The recent explosion of Orbital Sciences' Antares rocket hasn't changed plans for Orion's December launch.

Until new exploration missions were set, there was little point in keeping Orion except for the jobs it created, said Lori Garver, then NASA's deputy administrator and now head of the Air Line Pilots Association.

"What's it going to do? What's its mission?" she said. "Setting a design and a technology at a point in time when you don't know where you're going or when does not make a lot of sense."

Q. What happened?

Congress was angered by the administration's proposal, and Constellation contractors lobbied furiously against it.

A compromise deal preserved Orion and directed NASA to build a Saturn V-class rocket to launch it, called the Space Launch System, or SLS.

If astronauts ever do explore beyond low Earth orbit again, they'll need a spacecraft like Orion that can handle higher-speed re-entries through the atmosphere.

"Orion is a linchpin in our approach to become deep space explorers," said Bobby Braun, a Georgia Tech professor and former NASA chief technologist. "There have been bumps along the road."

Q. When will Orion fly a crew, and where to?

Be patient. After another unmanned test in 2018, the first launch of up to four astronauts from Kennedy Space Center is planned no sooner than 2021 atop NASA's 321-foot Space Launch System rocket.

The first crew might circle around the moon, but no decision has been made. By the mid-'20s, NASA hopes to launch a crew to an asteroid that has been robotically captured and tugged to an orbit near the moon where Orion can reach it.

The ogive panels, which protect the crew module from sound and vibration during ascent, were installed around the spacecraft just below the Launch Abort System tower.(Photo: NASA)

NASA says the Asteroid Redirect Mission will test systems and procedures needed to get to Mars, but there is skepticism in Congress and among scientists about its value and the extent to which it prepares for Mars.

The National Research Council report said NASA must establish more specific milestones on the path to Mars to develop technologies, show progress and keep teams sharp.

Q. Why is it taking so long?

From the start Orion was a complex design that had to support two very different missions: the ultimate goal of Mars, plus getting crews to the space station (no longer part of the plans).

Orion could have been finished sooner. But after a lull during the cancellation debate, its progress was tied to the Space Launch System rocket targeting launches in 2018 and 2021.

NASA arranged for the European Space Agency to provide Orion's next service module, which provides propulsion, power and life support systems. The deal made the program an international partnership, but ceded control over a major system.

As with any major new space vehicle, there are technical challenges to overcome.

"We have not had a human-rated re-entry system that could handle the speeds of anything beyond low Earth orbit since the Apollo days," said Georgia Tech's Braun. "The technical challenge of Orion should not be underestimated."

Orion is a large, heavy spacecraft that needs to shed up to 2,800 pounds by its next test flight in 2018, according to the U.S. Government Accountability Office.

Engineers have tracked a concern that the heat shield could form cracks. This week's test flight will provide data on the heat shield's performance, but not at the speeds and heating crews will experience.

Also slowing Orion's pace is flat annual funding. That spreads out the work, increasing the chance that issues will be discovered late in the development process and take more time and money to fix.

Cornell's Lunine said NASA's human exploration budget must grow slightly more than inflation.

"With flat funding, you just never make it to Mars," he said. "Very soon, the nation has got to make a decision about its ambitions with respect to human spaceflight."

Q. How much will Orion cost taxpayers?

NASA estimates it will cost between $8.5 billion and $10.3 billion to get Orion ready for its first flight with astronauts in 2021. That estimate, however, excludes nearly $6 billion spent before the Constellation program was canceled.

NASA is spending roughly $1 billion a year on Orion, which adds up. At least 15 years will pass from Orion's contract award in 2006 to the first crew launch.

Nearly 3,300 people work on Orion, including 625 civil servants and 2,650 contractors. That's in the same ballpark as the entire staffs at SpaceX, United Launch Alliance or Orbital Sciences.

Orion's cost stands in stark contrast to the commercial vehicles developed to launch cargo to the ISS and now being readied to fly astronauts as soon as 2017.

NASA spent $396 million to help SpaceX ready Falcon 9 rockets and Dragon capsules that have completed four station resupply missions. This week's test flight alone will cost $375 million.

NASA projects spending a total of about $5 billion to develop multiple commercial crew vehicles from start to finish, or a little more than half Orion's cost to reach its first test flight.

"What we have is a clash of cultures," said Garver. "It's OK, it's what we've got, but it is hard to understand the vast differences in money."

Q. Why not use the commercial capsules for exploration?

NASA's Commercial Crew Program recently selected Boeing and SpaceX capsules to fly astronauts to the ISS by 2017. But they aren't designed to fly beyond low Earth orbit, so can't be compared to Orion, engineers say.

"Orion is a very different capsule for a very different job," said Braun, calling Orion's engineering challenges "exceedingly more complicated."

A spacecraft returning from the moon must dissipate roughly twice as much energy as one returning from low Earth orbit, he said, requiring a heat shield designed for much higher speeds. The capsules also must fly in much tighter corridors, and their mass must be managed even more carefully.

Q. Is Orion the same as an Apollo capsule?

Orion shares a "blunt body" shape with Apollo capsules, but is significantly larger to carry four astronauts instead of three.

"It gives NASA a lot more flexibility in how we explore," said Mark Geyer, NASA's Orion program manager.

At 16.5 feet in diameter, Orion's heat shield is the largest ever built, more than 25% wider than an Apollo capsule's. Lead contractor Lockheed Martin says the capsule has the volume of two minivans.

"The shape looks old," said Mike Hawes, Lockheed's Orion program manager. "Everything about it is new."

Q. Why fly this test flight?

Exploration Flight Test-1 is primarily a test of Orion's crew module, specifically its heat shield, as it re-enters the atmosphere at 20,000 mph, or about 85% of the speed of a return from the moon, generating heating up to 4,000 degrees Fahrenheit. The flight will test separations of components including fairings and the launch abort system, and flight computers, parachutes and recovery operations, the latter led by Kennedy Space Center crews.

Aside from producing useful data, program managers fought for the test as a way to demonstrate progress and give teams operational experience and something to look forward to years before a crew flies.

Q. Can Orion continue to survive budget pressure and political changes?

NASA's Geyer said he expects the program to be reviewed during changes in political leadership.

The International Space Station overcame a cancellation threat early in its development and is now the centerpiece of NASA's human space program. More recently, Orion felt the heat.

"It survived that, and now we are here about to fly," said Geyer. "It's good design, it's a good team, it's a good mission, and now it's time to fly it."